Showing posts with label Acoustic Engineering. Show all posts
Showing posts with label Acoustic Engineering. Show all posts

What Does Speed Depend On

What does speed depend on - The speed of any wave depends upon the properties of the medium through which the wave is traveling. Typically there are two essential types of properties which affect wave speed - inertial properties and elastic properties.



Elastic properties are those properties related to the tendency of a material to maintain its shape and not deform whenever a force or stress is applied to it. A material such as steel will experience a very small deformation of shape (and dimension) when a stress is applied to it. Steel is a rigid material with a high elasticity.

What does speed depend on - On the other hand, a material such as a rubber band is highly flexible; when a force is applied to stretch the rubber band, it deforms or changes its shape readily. A small stress on the rubber band causes a large deformation. Steel is considered to be a stiff or rigid material, whereas a rubber band is considered a flexible material. At the particle level, a stiff or rigid material is characterized by atoms and/or molecules with strong attractions for each other.

When a force is applied in an attempt to stretch or deform the material, its strong particle interactions prevent this deformation and help the material maintain its shape. Rigid materials such as steel are considered to have a high elasticity. (Elastic modulus is the technical term). The phase of matter has a tremendous impact upon the elastic properties of the medium. In general, solids have the strongest interactions between particles, followed by liquids and then gases. For this reason, longitudinal sound waves travel faster in solids than they do in liquids than they do in gases. Even though the inertial factor may favor gases, the elastic factor has a greater influence on the speed (v) of a wave, thus yielding this general pattern: what does speed depend on

What does speed depend on


Inertial properties are those properties related to the material's tendency to be sluggish to changes in it's state of motion. The density of a medium is an example of an inertial property. The greater the inertia (i.e., mass density) of individual particles of the medium, the less responsive they will be to the interactions between neighboring particles and the slower that the wave will be.

What does speed depend on - As stated above, sound waves travel faster in solids than they do in liquids than they do in gases. However, within a single phase of matter, the inertial property of density tends to be the property which has a greatest impact upon the speed of sound. A sound wave will travel faster in a less dense material than a more dense material. Thus, a sound wave will travel nearly three times faster in Helium as it will in air. This is mostly due to the lower mass of Helium particles as compared to air particles.

The speed of a sound wave in air depends upon the properties of the air, namely the temperature and the pressure. The pressure of air (like any gas) will affect the mass density of the air (an inertial property) and the temperature will affect the strength of the particle interactions (an elastic property). At normal atmospheric pressure, the temperature dependence of the speed of a sound wave through air is approximated by the following equation:

v = 331 m/s + (0.6 m/s/C)•T

where T is the temperature of the air in degrees Celsius. Using this equation to determine the speed of a sound wave in air at a temperature of 20 degrees Celsius yields the following solution.
v = 331 m/s + (0.6 m/s/C)•T
v = 331 m/s + (0.6 m/s/C)•(20 C)
v = 331 m/s + 12 m/s
v = 343 m/s

hat does speed depend on (The above equation relating the speed of a sound wave in air to the temperature provides reasonably accurate speed values for temperatures between 0 and 100 Celsius. The equation itself does not have any theoretical basis; it is simply the result of inspecting temperature-speed data for this temperature range. Other equations do exist which are based upon theoretical reasoning and provide accurate data for all temperatures. Nonetheless, the equation above will be sufficient for our use as introductory Physics students.)

Read too :

Deriving The Wave Equation | Wave Equation In Fluid Dynamics

Deriving The Wave Equation So far in this book we have dealt with vibrations. These are processes that vary as functions of time.We were able to describe relevant types of vibrations with common differential equations. 


Deriving The Wave Equation


This chapter now focuses on waves, which are processes that vary with both time and space. Their mathematical description requires partial differential equations. Motivated by the electroacoustic analogies, we start this chapter with an excursion into electromagnetic waves. This excursion will bring us back to sound waves in the next section1Deriving The Wave Equation

The Wave Equation in Fluids


Equivalent circuit for a differential section of a homogeneous, lossless electrical transmission line
Figure 7.1 illustrates the equivalent circuit for a elementary section of a homogeneous,
lossless electrical transmission line. For this section, the following loop and node equations hold, 7 The Wave Equation in Fluids

The Wave Equation in Fluids


The following two linear differential equations are obtained by neglecting  higher-order differentials, This set of equations shows that a temporal variation of the slope of one of the variables results in a proportional spatial variation of the slope of the other. This causes that the total energy on the line swings between two types  of complementary energies, namely,


Deriving The Wave Equation

• magnetic energy per length, W_ = 1  2L_ i2
• electric energy per length, W_ = 1   2C_ u2
The two linear differential equations (7.3) can be combined into a differential equation of second order, which is

The Wave Equation in Fluids
This is the so-called wave equation, here in the formulation for electromagnetic  waves on an electrical transmission line. Hereby c line, el is the propagation speed of electromagnetic waves on the transmission line, namely,
In acoustics we also have waves that propagate along one coordinate, for example, in gas-filled tubes with small diameters compared to wavelength.Such longitudinal compression waves are schematically sketched in Fig
Deriving The Wave EquationOne-dimensional longitudinal acoustic wave. Zones of compression and rarefaction are schematically indicated Two complementary forms of energies are as well required for these types of waves to occur, but in this case we choose energies per volume to be compatible  with the use of p and v as characteristic sound-field quantities. We thus get  7.1 Derivation of the One-Dimensional Wave Equation 89
  • potential energy per volume, W__ = 1 2κp2 κ ...volume compressibility
  • kinetic energy per volume, W__ = 1 2_ v2 _ ...mass density

Mimicking the wave equation for the electromagnetic waves, we now suggest the following wave equations for one-dimensional acoustic waves,

and the combined second order expression as
with the propagation speed of sound waves to be
The pressing question now is whether these supposed equations, which are  so neatly analogous to electric expressions, are actually in compliance with physical reality. 

The answer is yes, at least approximately. Yet, there are a number of features of the media where sound exists that must be idealized. The following section will elaborate on them. Deriving The Wave Equation

Sourch : Acoustic Engineering Book